According to data analyzed by Climate Central, "in Tokyo, July and August average temperatures have warmed by 2.7°F since the last time the Olympics were held there in 1964." Also noted by Climate Central, there are on average 8 more days over 95 in Tokyo now than when the last summer Olympics were held.
Tokyo's coastal position and latitude make for a humid subtropical climate zone. This is very similar in climate to the southeastern United States. Tokyo typically sees hot and humid summer with cooler winters with occasional cold snaps.
Tokyo is also the largest city in the entire world. The urban heat island effect has been a large contributor to warming in the city.
According to the city's Bureau of Environment, the city has warmed by about 3 degrees Celsius in the last 100 years, with the culprits being global climate change and the urban heat island effect of this mega-metropolis.
The city notes measures it is taking to reduce the risk of heat illness for tourists and citizens, including creating cool spots in the city and the tradition of "uchimizu" where water is sprinkled on the sidewalks to cool them down.
Heat Index values will be into the 90s during the first few days of the games. The main hazard, in this case, will be extreme humidity which does now allow the body to effectively cool itself by sweating.
Spectators are no longer allowed at the games so the risk for heat illness in the stands isn't as high of a concern now. But, athletes do face a very real threat of heat illness this year.
The marathon this year was moved to Sapporo, a cooler city to the north of Tokyo.
Most of the summer sports will take place outdoors this year. Those athletes at the highest risk for heat illness are those who exert the most energy, are outside for a long duration, and have the least amount of downtime.
According to recent research, a few of the sports at the highest risk are the triathlon, marathon, tennis, and hockey.
To counteract the threats, some athletes have been acclimating in warmer climates this month, cooling stations have been implemented by the International Olympic Committee, and athletes will be drinking and immersing themselves in cold water before, during, and after events.